There are three main purposes of the studies proposed in this application: (1) to develop and validate a third generation coronary Doppler velocity probe; (2) to expand the capabilities of our existing third generation aortic Doppler velocity probe to make the instrument have bi-directional capability and (3) to utilize these unique Doppler instruments to pursue important physiological questions. Third generation Doppler probes have several unique capabilities. By simultaneously sampling 16 equidistant gates across the vessel lumen, velocity profiles can be obtained. Furthermore, this data can be used to measure changes in vessel diameter continuously. Finally, integrated volumetric flow can be calculated. Because the probes are light (less than 10 grams) and tiny (3-5 mm) they can be affixed with gentle suction to coronary vessels or the aorta of patients at the time of open-heart surgery. Our laboratory is at the forefront in the design and implementation of this new exciting technology. Once these instruments have been validated with in vitro and animal experiments, we will utilize them to pursue the following questions: (1) Is the severe depression in coronary reactive hyperemia observed in patients with cardiac hypertrophy related to an increase in resting coronary flow? (2) Is the depression in coronary reactive hyperemia observed in the early period following cardiopulmonary bypass related to an increase incoronary flow? (3) What are the effects of a coronary stenoses on the flow field downstream the obstruction? Do disturbances in the flow field contribute to the pathogenesis of atherosclerotic changes in the vessel wall downstream from the stenoses? (4) What are the effects of aortic stenoses and aortic valvular prosthesis on velocity profiles in the aorta under varying conditions? In addition, our improved third generation aortic velocity Doppler probe will be utilized to permit cardiac surgeons to quantitatively assess the severity of aortic regurgitation at surgery and most importantly, to continuously monitor ascending aortic flow throughout the operative and early post operative periods. Such data should lead to substantive improvements in the intraoperative management of patients having open-heart surgery.